High-sensitivity pressure conduction sensor for localized pressures and stresses

ABSTRACT

A high-sensitivity pressure conduction sensor is presented. The present invention includes a pair of locally resilient conductive layers and a locally resilient pressure conduction composite disposed between and contacting both conductive layers. Alternate embodiments include at least three locally resilient conductive layers and at least two locally resilient pressure conduction composites, each having a critical percolation threshold. Each composite is disposed between and contacting two conductive layers in a multi-layer fashion. Other embodiments include a locally resilient pressure conduction composite, a flexible substrate completely surrounding the composite so as to seal it therein, and a pair of electrical leads contacting the composite and terminating outside of the flexible substrate. Pressure conduction composites are composed of a plurality of conductive particles electrically isolated within a non-conductive matrix. Conductive particles are loaded so as to have a volume fraction approaching the critical percolation threshold of the material system and exhibit a conductance that greatly increases with pressure. Sensors may be arranged to form one or more arrays including planar and conformal configurations. The present invention has immediate application in keyboards, intrusion systems, control systems, submarines, ships, sonobuoys, doors, and switches.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims priority under 35 U.S.C. §119(e) from U.S. Provisional Patent Application No. 60/512,335 filedOct. 17, 2003, entitled Pressure Conduction Devices, the contents ofwhich are hereby incorporated by reference.

FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

None.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a device capable of largeconduction changes when locally compressed and decompressed.Specifically, the present invention is a sensor of sufficiently highsensitivity so as to enable pressure and stress measurements.

2. Description of the Related Art

Sensors are critical to the performance of keyboards, intrusiondetection systems, and fluid control systems.

Musical keyboards employ carbon contacts to detect the depression of akey and a capacitive strip to measure how hard and fast the key isdepressed so as to simulate the dynamic response of an instrument. Keysare susceptible to dirt, moisture, and other contaminants. Mechanicalsolutions adversely effect pressure detection and penalize the dynamicrange of the instrument.

Intrusion systems include optical and laser devices for detectionpurposes. Devices are difficult to conceal and readily defeatable.Furthermore, such systems are limited in their mapping capability andtherefore do not provide a complete record of an intrusion, including,but not limited to, location and time, to resolve direction of traveland speed.

Fluid control systems for cooling, fire suppression, and fuel transportrequire inline sensors to accurately measure pressure for the activecontrol of valves and pumps. However, such systems must function withina harsh environment including rapidly changing pressures.Diaphragm-based gages offer reliable pressure measurement, even whensurrounded by corrosive and high temperature fluids, but are generallytoo bulky for inline use. Furthermore, low sensitivity and high costlimit the application of diaphragm-based devices to all but the mostcritical systems.

High-sensitivity pressure sensors are sorely needed for the abovereferenced applications, as well as for other applications, includingsubmarines, torpedoes, sonobuoys, industrial and commercial keyboards,doors, and switches. Composites having one or more pressure variableproperties are critical to a new class of sensors for use within theapplications above.

Polymer-metal composites having variable resistance are described inU.S. Pat. No. 4,028,276. Compositions experience an actual change inelectric properties, namely, resistance, when compressed by a mechanicalload. Practical applications of these materials require a complete anduniform compression of the composite cross its presented area. As such,a large force is required for proper function. Resultantly,polymer-metal composites lack the fidelity necessary to accuratelymeasure pressure and stress and thereby limited to sensing grossmagnitudes and differentials.

Pressure conduction composites exhibit a change in conductance inresponse to a mechanical load. Unlike polymer-metal composites, pressureconduction composites do not experience an actual resistance change.Rather, compression alters the spatial arrangement of conductiveparticles within a non-conductive matrix as so to enable a change inconduction between particles about the critical percolation threshold ofthe material system. Small localized mechanical loads or pressures causea very large change in the “effective” resistance at the output of thecomposite. This highly localized sensitivity greatly improves thesignal-to-noise ratio and usable signal strength from the composite.Furthermore, pressure conduction composites are inherently resistant tothe deleterious effects of dirt, moisture, and other contaminants.

Therefore, what is currently required is a high-sensitivity sensorincluding a pressure conduction composite capable of detecting andmeasuring pressure and/or stress.

Furthermore, what is currently required is a high-sensitivity sensorincluding a pressure conduction composite that is sufficiently robust toavoid the deleterious effects of harsh environments.

Furthermore, what is currently required is a high-sensitivity sensorincluding a pressure conduction composite having a compact, conformalform of minimal volume.

Furthermore, what is currently required is a high-sensitivity sensorincluding a pressure conduction composite that is easily configurable toenable a matrix arrangement for large spatial applications.

SUMMARY OF INVENTION

An object of the present invention is to provide an electrically andmechanically simple sensor that minimizes signal-processingrequirements.

A further object of the present invention is to provide a sensor that issufficiently robust to avoid the deleterious effects of harshenvironments.

A further object of the present invention is to provide a sensor havinga compact, conformal form of minimal volume.

A further object of the present invention is to provide a sensor that iseasily configurable into a matrix arrangement for large spatialapplications.

In its simplest form, the present invention is comprised of a pair oflocally resilient conductive layers and a locally resilient pressureconduction composite disposed between and contacting both conductivelayers.

In alternate embodiments, the present invention may include at leastthree locally resilient conductive layers and at least two locallyresilient pressure conduction composites, each having a criticalpercolation threshold. Each composite is disposed between and contactingtwo locally resilient conductive layers in a multi-layered fashion.

In yet other embodiments, the present invention may include a locallyresilient pressure conduction composite, a flexible substrate completelysurrounding the composite so as to seal it therein, and a pair ofelectrical leads contacting the composite and terminating outside of theflexible substrate.

Composites are composed of a plurality of conductive particleselectrically isolated within a non-conductive matrix. Conductiveparticles are loaded at a volume fraction approaching the criticalpercolation threshold of the material system so as to exhibit aconductance that greatly increases with pressure. Passive and activebiasing may be applied via a variety of mechanical, electromechanical,and magnetic devices. Sensors may be arranged to form an arrayarchitecture including planar and conformal configurations.

The term “locally resilient” refers to the movement of composite andlayers immediately adjacent to a mechanical load. For example, acompression event includes a volumetric reduction of the matrix andlocalized elastic deformation of the outer layers. A decompression eventincludes a volumetric expansion of the matrix and localized elasticrecovery of the outer layers.

The flexible and pliable composites within the present invention are thefunctional equivalent of a highly pressure responsive resistor. Sincecomposites may be tailored to a variety of pressure ranges, compositesmay be color coded to visually identify performance characteristics.

The described invention provides several advantages over the relatedarts. The invention is inherently more sensitive resulting in moreaccurate and detailed measurements. The noise component within theusable signal from the present invention is far lower than conventionalsensors. The invention is extremely rugged, inexpensive, scalable insize and form, flexible and conformal, and amenable to conductive andnon-conductive coatings to improve durability in harsh environments.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail, by way of exampleonly, with reference to the accompanying drawings, in which:

FIG. 1 a is a schematic diagram showing a pressure conduction composite,composed of a non-conductive matrix having conductive particleselectrically isolated therein, sandwiched between a paired arrangementof conductive and optional non-conductive layers.

FIG. 1 b is a schematic diagram showing sensor from FIG. 1 a afterlocalized compression of the composite so as to allow electricalconnectivity between particles adjacent thereto.

FIG. 2 is a graph showing force dependent resistance for severalexemplary titanium-diboride/polymer systems.

FIG. 3 is a perspective view of a pressure conduction composite withperforations so as to enhance compression and expansion properties ofthe composite.

FIG. 4 is a section view of a sensor having a multi-layer arrangementincluding pressure conduction composite layers bounded by conductivelayers with optional non-conductive outer layers.

FIG. 5 is a section view of a sensor having a pressure conductioncomposite hermetically sealed between a pair of flexible substrates withelectrical leads thereon.

FIG. 6 is an exemplary electrical circuit used to extract and processvoltage data from a sensor for the measurement of pressure and stress.

FIG. 7 is an exemplary circuit diagram showing sampling circuit withwire and wireless transmission capabilities.

FIG. 8 is a section view of a sensor contacting and attached to a rigidelement.

FIG. 9 is a partial section view showing an exemplary application of thepresent invention within a fluid or gas filled pipe.

FIG. 10 is a top view showing an exemplary application having aplurality of sensors arranged in an array along a rigid structure.

REFERENCE NUMERALS

-   1 Sensor-   2 Pressure conduction composite-   3 Conductive particle-   4 Matrix-   5 Conductive layer-   6 Conductive layer-   7 Force-   13 Pressure conduction composite-   14 Thickness-   15 Perforations-   16 Multi-layer sensor-   17 a-17 b Outer conductive layer-   18 a-18 c Inner conductive layer-   19 a-19 d Pressure conduction composite-   20 Sensor-   21 Outer layer-   22 Outer layer-   23 Pressure conduction composite-   24 Electrical lead-   25 Electrical lead-   30 Resistor-   31 Buffer-   32 Communications circuit-   34 Interface circuit-   35 Microcontroller-   36 Wire interface-   37 Wireless interface-   38 Sensor-   39 Rigid structure-   40 Force-   41 Valve-   42 Pipe-   43 Pipe wall-   44 Electrical leads-   45 Communications circuit-   46 Sensor-   47 Interior surface-   48 Exterior surface-   49 Sensor-   50 Rigid element-   26 Electrical contact-   27 Electrical contact-   28 Seam-   29 Sensor-   51 Non-conductive layer-   52 Non-conductive layer-   53 Non-conductive layer-   54 Non-conductive layer.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1 a, a schematic representation of one embodimentof the sensor 1 is shown having a pressure conduction composite 2disposed between two conductive layers 5, 6. An optional pair ofnon-conductive layers 51 and 52 contact the conductive layers 5 and 6,respectively, opposite of the pressure conduction composite 2.

Conductive layers 5, 6 include a variety of materials, such as metalsand composites, and a variety of generally planar structures, includingplates, foils, films, foams, weaves, and braids. The pressure conductioncomposite 2 is composed of conductive particles 3 within anon-conductive yet pliable and resilient matrix 4. The matrix 4 is agenerally planar solid that surrounds and isolates the conductiveparticles 3 so as to maximize resistance and minimize conductancethereby preventing current flow between conductive layers 5, 6 at anambient or biased pressure. Non-conductive layers 51, 52 isolate thesensor 1 so as to prevent electrical current loss from the sensor 1 andto shield the sensor 1 from electrical current external to the device.Non-conductive layers 51, 52 include a variety of non-conductingmaterials, such as polymers and composites, and a variety of generallyplanar structures, including plates, foils, films, foams, weaves, andbraids. It is preferred for conductive layers 5, 6 and non-conductivelayers 51, 52 to be pliable.

Referring now to FIG. 1 b, the distance between conductive particles 3decreases with increasing force 7 thereby increasing the effectiveconductance of the pressure conduction composite 2. In the presentinvention, force 7 is a mechanical load partially interacting with atleast one conductive layer 5, 6 and optionally with at least onenon-conductive layer 51, 52, as represented in FIG. 1 b. Maximumconductance is achieved when conductive particles 3 and conductivelayers 5, 6 are contacting. The matrix 4 should be sufficientlyresilient to allow for its recovery after the force 7 is removed. It ispreferred for the conductive particles 3 to return to their original ornearly original location within the matrix 4.

The term “locally resilient” refers to the movement of the pressureconduction composite 2, one or more surrounding conductive layers 5, 6,and one or more optional non-conductive layers 51, 52 under and adjacentto a mechanical load. For example, a compression event includes avolumetric reduction of the matrix 4, spatial displacement of conductiveparticles 3, and localized elastic deformation of conductive layers 5, 6and nonconductive layers 51, 52. A decompression event includes avolumetric expansion of the matrix 4 to its original or nearly originalvolume, spatial displacement of conductive particles 3 to their originalor nearly original locations, and localized elastic recovery ofconductive layers 5, 6 and nonconductive layers 51, 52. Compression anddecompression may be assisted by a variety of mechanical,electromechanical, and magnetic devices.

Referring now to FIG. 2, resistance-force curves are shown for severalexemplary pressure conduction composites 2 having titanium diborideparticles within a polymer plate. In general, pressure conductioncomposites 2 exhibit an extremely large decrease in resistance over arelatively small range of force. The volume fraction of conductiveparticles 3 influences the resistance-to-force characteristics of thecomposition thereby allowing the material system to be tailored or tunedfor ambient and operating pressures. It is likewise possible for thepressure conduction composite 2 to be actively biased as a function ofconstant or changing ambient pressure thereby requiring minimal pressureto produce the desired change in conductance.

Referring again to FIG. 1 a, stoichiometry, thickness, and feedstockmaterials greatly influence the resistance-force profile via theproperties of sensitivity, signal quality, and pressure range.Stoichiometry relates to the density of particles 3 within the matrix 4.The size and density of particles 3 greatly influence the sensitivityand pressure range. Thickness of the pressure conduction composite 2,conductive layers 5, 6 and non-conductive layers 51, 52 determine thepliability of the sensor 1 and its ability to couple mechanical loadsinto the material system. In general, it is preferred to have conductiveparticles 3 at a volume fraction at or near the critical percolationthreshold of the material system. Furthermore, it is generally preferredto have the conductive particles 3 randomly dispersed within the matrix4 so as to avoid a continuous path between conductive layers 5, 6 atinitial conditions. Likewise, it is preferred for matrix 4, conductivelayers 5, 6 and non-conductive layers 51, 52 to be sufficiently thin soas to insure a low profile, flexible sensor 1 for conformalapplications.

The critical percolation threshold is the pressure at and above whichthe pressure conduction composite 2 exhibits a very large decrease inresistance, which may be as large as six orders of magnitude. Pressuresnear yet less than the critical percolation threshold ensure theconducting particles 3 to have a spatial separation sufficiently smallso as to allow current flow between the conducting layers 5, 6. Pressureconduction composites 2 operating near the critical percolationthreshold ensure a sufficiently distinctive change in conduction over arange of pressures so as to allow for the precise measurement ofpressure and/or stress.

The matrix 4 may be composed of one or more electrically resistive,compressible and resilient materials including, but not limited to,polymers and elastomers. It is preferred for the matrix 4 to betemperature resistant. Exemplary materials include formulations ofpolyethylene, polystyrene, polyvinyldifluoride, polyimide, epoxy,polytetrafluorethylene, silicon rubber, polyvinylchloride, andcombinations thereof. Preferred embodiments of the present inventionwere composed of the elastomer RTV R3145 manufactured by the Dow CorningCompany.

Conductive particles 3 may include one or more electrically conductivematerials including, but not limited to, metals, metal-based oxides,nitrides, carbides, and borides, and carbon black. It is preferred thatconductive particles 3 resist deformation when compressed and have amelt temperature sufficiently above the thermal conditions generatedduring current flow and interrupt. Exemplary materials include aluminum,gold, silver, nickel, copper, platinum, tungsten, tantalum, iron,molybdenum, hafnium, combinations and alloys thereof, Sr(Fe,Mo)O3,(La,Ca)MnO3, Ba(Pb,Bi)O3, vanadium oxide, antimony doped tin oxide, ironoxide, titanium diboride, titanium carbide, titanium nitride, tungstencarbide, and zirconium diboride.

The pressure conduction composite 2 is fabricated via known methods. Forexample, the pressure conduction composite 2 may be prepared fromhigh-purity feedstocks, mixed, pressed into a solid, and suffused withoil. Conductive layers 5, 6 are thereafter bonded to the pressureconduction composite 2 via an adhesive or vulcanization process. It waspreferred to adhesively bond conductive layers 5, 6 to the pressureconduction composite 2 via an electrically conductive epoxy.Non-conductive layers 51, 52 are likewise bonded to the conductivelayers via a thermally resistant adhesive, preferably a pliable epoxy.

Feedstocks include both powders and liquids. Conductive particles 3 wereexclusively solid particulates. For example, it was preferred for thefeedstock comprising the conductive particles 3 to be a fine, uniformpowder, examples including 325-mesh titanium diboride and titaniumcarbide. The non-conductive matrix 4 was fabricated with either a fine,uniform powder or a liquid with sufficient viscosity to achieve adequatedispersion of conductive particles 3 after mixing. Powder-basedformulations were mechanically mixed and compression molded usingconventional methods. Polytetrafluorethylene and other polymers mayrequire sintering within an oven to achieve a structurally durablesolid. Powder-liquid formulations, examples including titanium diborideor titanium carbide and a silicone-based elastomer, were vulcanized andhardened within a die under low uniaxial loading at room temperature.

In some embodiments, it may be desired to impregnate the pressureconduction composite 2 with a liquid via a method referred to assuffusion. The pressure conduction composite 2 is submerged within abath of one or more inorganic oils, preferable silicone based, therebyallowing complete infiltration of the liquid into the otherwise solidpressure conduction composite 2. The exposure time of the pressureconduction composite 2 is influenced by the dimensional properties andcomposition of the solid. For example, a pressure conduction composite 2having a thickness of 0.125-inch, a width of 0.200-inch, and a length of0.940-inch and composed of titanium diboride or titanium carbide at avolume fraction of 66 percent and RTV R3145 at a volume fraction of 34percent was adequately suffused after a 48 hour period.

Conductive layers 5, 6 and non-conductive layers 51, 52 are adhered tothe pressure conduction composite 2 either before or after suffusion. Ifbefore suffusion, conductive layers 5, 6 and non-conductive layers 51,52 are placed within a die along with sufficiently mixed compositioncomprising the pressure conduction composite 2 in the desired sequentialorder. For example, a matrix 4 composed of a silicone elastomer wasadequately bonded to two 0.020-inch thick brass plates and polymernon-conductive layer 51, 52 by curing the otherwise liquid elastomer atroom temperature between 3 to 24 hours or at an elevated temperaturebetween 60 to 120 degrees Celsius for 2 to 10 hours. If after suffusion,a silicone adhesive is applied between pressure conduction composite 2and conductive layers 5, 6 and non-conductive layers 51, 52 andthereafter mechanically pressed until the adhesive is cured.

In some embodiments, it may be advantageous for the pressure conductioncomposite 2 to be porous. Porosity may be required to tailor themechanical stiffness, elastic properties and cooling characteristics ofthe pressure conduction composite 2 without adversely degradingelectrical conductance and resistance of the element. Furthermore,porosity may improve the compliance and sensitivity of the sensor 1.

Pores may include a variety of shapes including, but not limited to,spheres, ellipsoids, cylinders, and irregular shapes. Referring now toFIG. 3, an exemplary planar disposed pressure compression composite 13is shown having a plurality of cylindrically shaped perforations 15traversing the thickness 14 of the element. The dimensions and spatialdistribution of the perforations 15 are used to achieve the desiredmechanical and electrical characteristics.

Pores may be formed by a variety of manufacturing methods. For example,cavities may be mechanically drilled into the pressure conductioncomposition 13. Pores may be introduced during mixing of matrix 4 andconductive particles 3 feedstocks via the introduction of gas bubbles.It is likewise possible to include microspheres composed of either alow-density foam or a gas or fluid filled spheres during the mixingprocess. Also, cavities may be formed during curing of the matrix 4 inan oven whereby localized heating and phase transitions yield voidformation and growth.

In yet other embodiments, it may be advantageous to apply a waterproofor heat resistant coating known within the art over sensors 1 describedherein to prevent direct contact with the surrounding medium.

A more complex embodiment of the sensor 1 in FIGS. 1 a and 1 b mayinclude two or more pressure conduction composites 2 bounded by three ormore conductive layers 5 or 6 where the outermost conductive layers 5 or6 each contact an optional non-conductive layer 51 or 52 opposite of thepressure conduction composite 2.

Referring now to FIG. 4, an exemplary planar disposed embodiment isshown having four pressure conduction composites 19 a-19 d separated bythree inner conductive layers 18 a-I 8 c and bounded by a pairedarrangement of an outer conductive layer 17 a or 17 b and anon-conductive layer 53 or 54. Materials and fabrication methodsdescribed above are applicable to this embodiment.

Inner conductive layers 18 a-18 c physically and electrically separateadjacent pressure conduction composites 19 a-19 d within the multi-layersensor 16. A voltage is selectively applied to one or more outerconductive layers 17 a, 17 b and inner conductive layers 18 a-18 c so asto allow for current flow to one or more outer conductive layers 17 a,17 b and/or one or more inner conductive layers 18 a-18 c. Current flowacross one or more pressure conduction composites 19 a-19 d may bearranged to form a conduction logic circuit facilitating two or moresensitivity ranges for pressure and stress. For example, it may bedesired to have two or more pressure conduction composites 19 a-19 dtuned to one or more separate pressure-conduction or stress-conductionranges. The multi-layer sensor 16 in FIG. 4 may have a voltage appliedto both outer conductive layers 17 a and 17 b and the center innerconductive layer 18 b so as to achieve four conduction pathways.Compression of the pressure conduction composite 19 a allows currentflow between outer conductive layer 17 a and inner conductive layer 18a. Compression of the pressure conduction composite 19 b allowscurrently flow between inner conductive layers 18 b and 18 a.Compression of the pressure conduction composite 19 c allows currentlyflow between inner conductive layers 18 b and 18 c. Compression of thepressure conduction composite 19 d allows currently flow between outerconductive layer 17 b and inner conductive layers 18 c. A variety ofother conduction logic circuits are apparent from the example above.

Referring now to FIG. 5, it may be advantageous in some applications tohave the pressure conduction composite 23 sealed from the surroundingenvironment. In this embodiment, the sensor 20 is shown having apressure conduction composite 23 disposed between and electricallycontacting a pair of electrical leads 24 and 25 and thereafter between apair of outer layers 21 and 22. Materials and fabrication methodsdescribed above are applicable to this embodiment.

It is preferred for the outer layers 21 and 22 to be composed of aflexible, thermally resistant, and non-conducting material, one examplebeing a polyimide. Outer layers 21 and 22 completely cover and surroundthe pressure conduction composite 23 and electrical leads 24 and 25 soas to prevent their contact with the surrounding environment. Outerlayers 21 and 22 are joined via an adhesive or thermally bonded so as toprovide a continuous seam 28 about their mutual perimeters. Electricalcontacts 26 and 27 are electrically connected to the electrical leads 24and 25, respectively, and traverse the seam 28 between outer layers 21and 22 without compromising the seal there between. Electrical contacts26, 27 facilitate communication of sensor 20 data to acquisitionequipment.

In preferred embodiments, the pressure conduction composite 23 washermetically sealed between a pair of Kapton® thin films, sold by theDuPont Corporation, having copper traces and contact pads along one sidethereon so as to form the electrical contacts 26 and 27. Contact padsmechanically and electrically contacted the pressure conductioncomposite 23 within the sensor 20. Traces and pads were pre-etched ontothe Kapton thin film via known flex circuit techniques. Kapton outerlayers 21 and 22 were adhered to the pressure conduction composite 23via a conductive silver epoxy. A pair of pads was provided along thethin film opposite of the pads contacting the pressure conductioncomposite 23 so as to form the electrical contacts 26 and 27.

The sensor 1 in FIG. 1 a, multi-layer sensor 16 in FIG. 4, and sensor 20in FIG. 5 each require electrical connectivity to a circuit for thepurpose of data retrieval and interpretation. Referring now to FIG. 6, asensor 29, exemplary of the described devices above, is shown within adivider circuit, although a variety of other circuit designs arepossible. The sensor 29 is electrically connected at one end to aresistor 30 in a serial arrangement. The second end of the sensor 29 andresistor 30 are electrically connected to a voltage source of knownmagnitude, one example being a battery. A buffer 31 is electricallyconnected at one end between the sensor 29 and resistor 30 at node “A”and at the other end to a communications circuit 32. As described above,the sensor 29 has zero conduction and nearly infinite impedance when nomechanical load is applied across the sensor 29. As such, the voltage atnode “A” is zero. The conductance of the sensor 29 increases from zeroas a mechanical load of increasing magnitude is applied. The increasingconductance causes the voltage at node “A” to increase accordingly.Thereafter, the voltage at node “A” is amplified and/or filtered by acommercially available buffer 31 and communicated to a communicationscircuit 32.

The type, density, size, and mass fraction of the conductive particles 3and matrix 4 within the pressure conduction composite 2 determine thefunctional relationship between pressure and voltage at node “A”. Forexample, it is possible for the pressure conduction composite 2 tocommunicate a voltage that is linearly proportional to the mechanicallyapplied pressure within the sensor 29. Likewise, it is possible for thepressure conduction composite 2 to communicate a voltage that isnon-linear in relation to the applied pressure. However, it waspreferred for the change in conductance to be sufficiently large so asto be distinguishable from electrical noise within the circuit tominimize signal filtering and amplification.

Referring now to FIG. 7, one possible embodiment of the communicationscircuit 32 in FIG. 6 is shown including an interface circuit 34electrically connected to a microcontroller 35, thereafter electricallyconnected to a wire interface 36 and/or a wireless interface 37. Theinterface circuit 34 amplifies and/or filters the voltage output fromthe sensor 29 in FIG. 6 prior to the microcontroller 35. Themicrocontroller 35 converts the now analog signal to a digital signal,via an analog-to-digital converter (ADC), samples the signal, andorganizes the sampled signal data prior to its communication to the wireinterface 36 and/or wireless interface 37. The communications circuit 32may be directly embedded onto or within the sensor 29 or separatelydisposed so as to provide a smart network of sensors 29 communicating toa master controller. Direct coupling between communications circuit 32and sensor 29 allows the sensor 29 to also function as a heat sink.

While a variety of commercially available microcontrollers 35 areapplicable to the present invention, the MPS430 sold by TexasInstruments, Inc. contains onboard ADCs and communications interfacerequired for remote data uploading to a master controller. The MPS430supports a variety of asynchronous serial communication protocolscompatible with the present invention.

The wire interface 36 may be attached to the MPS430 controller as aflexible Serial Communications Interface (SCI). The SCI allows for bothsynchronous and asynchronous communication protocols, including RS-232,RS422, RS485, SPI and I2C.

The wireless interface 37 may include, by way of example, a Wi-Portmodule sold by Lantronix, Inc. capable of communicating data in anasynchronous format over an 802.11b Ethernet network. The Wi-Port alsocontains internal firmware allowing connection to a variety of TCP/IPprotocol stacks including ARP, UDP, TCP, ICMP, Telnet, TFTP, AutoIP,DHCP, HTTP, and SNMP with or without 128 bit WEP encryption for securitypurposes.

In some applications, it may be advantageous to limit externalmechanical loads to one surface along the sensor 38. Referring now toFIG. 8, a sensor 38, exemplary of those described herein, is showncontacting a rigid structure 39 along one surface and having a force 40applied onto the opposite surface. It is preferred for the sensor 38 tobe electrically isolated from the rigid structure 39 via either anon-conductive layer 51, as described above, or a non-conducting epoxyapplied between sensor 38 and rigid structure 39. A solid, fluid, or gasimpinges the surface opposite of the rigid structure 39 therebyproviding either a point or distributed mechanical load.

Referring now to FIG. 9, a sensor 46, exemplary of the devices describedherein, is shown within a pipe 42 at two locations about a valve 41 todemonstrate one specific application of the present invention. Thepliable nature of the sensor 46 allows it to conform to the contour ofpipe 42. Sensors 46 are bonded via a non-conductive adhesive to theinterior surface 47 of the pipe wall 43. A hole is provided through thepipe wall 43 immediately adjacent to the sensor 46 so to allow thesensor 46 to cover and seal the hole and prevent leakage from the pipe42. Electrical leads 44, similar to those described above, traverse thehole and electrical connects the sensor 46 to a communications circuit45, as described above. Likewise, the communications circuit 45 may bebonded via a non-conductive adhesive to the exterior surface 48 of thepipe wall 43 to further present leakage from the pipe 42. Two or moresensor 46 may be located within the pipe 42 so as to measure and recordpressure, pressure drop, and flow.

The low profile and compactness of the present invention lend itself toarrayed configurations. Referring now to FIG. 10, a plurality of sensors49 may be applied along a planar or non-planar rigid element 50 so as toprovide a two-dimensional array. Individual sensors 49 are electricallyconnected so as to communicate conductance data to a central computervia a row-column architecture similar to that used to control flat paneldisplays and to control active devices. The latter control architectureis described by the present inventors in co-pending U.S. patentapplication Ser. No. 10/823,237, entitled Matrix Architecture SwitchControlled Adjustable Performance Electromagnetic Energy CouplingMechanisms using Digital Controlled Single Source Supply, co-pendingU.S. patent application Ser. No. 10/872,974, entitled Thin, NearlyWireless Adaptive Optical Device, and co-pending U.S. application Ser.No. 10/894,150, entitled Pressure Sensitive Sensor for Real-TimeReconfigurable Sonar Applications, the contents of which areincorporated by reference.

The rigid element 50 may include a keyboard housing or a floor. In theformer application, sensors 49 are applied to the housing so as toprovide a plurality of touch sensitive keys or interact withconventional keys. In the latter application, sensors 49 are applied toa floor to form an intrusion detection system. Sensors 49 may be coveredby carpet or have an exterior finish representing a specific floor typeand style. An intruder activates individual sensors 49 within the floorvia the progression of footsteps. Individual signals from the sensors 49are thereafter communicated via wire or wireless means to a centralcomputer so as to provide location, path and speed data to securitypersonnel.

The description above indicates that a great degree of flexibility isoffered in terms of the present invention. Although the presentinvention has been described in considerable detail with reference tocertain preferred versions thereof, other versions are possible.Therefore, the spirit and scope of the appended claims should not belimited to the description of the preferred versions contained herein.

1. A high-sensitivity sensor comprising: (a) a pair of locally resilientconductive layers; and (b) a locally resilient pressure conductioncomposite having a critical percolation threshold, said locallyresilient pressure conduction composite comprising a non-conductivematrix and a plurality of conductive particles near said criticalpercolation threshold, said locally resilient pressure conductioncomposite disposed between and contacting said locally resilientconductive layers.
 2. The high-sensitivity sensor of claim 1, furthercomprising: (c) a rigid element contacting one said locally resilientconductive layer opposite of said locally resilient pressure conductioncomposite.
 3. The high-sensitivity sensor of claim 1, furthercomprising: (c) a pair of locally resilient non-conductive layers, eachsaid locally resilient non-conductive layer contacting one said locallyresilient conductive layer opposite of said locally resilient pressureconduction composite.
 4. The high-sensitivity sensor of claim 3, furthercomprising: (d) a rigid element contacting one said locally resilientnon-conductive layer opposite of said locally resilient conductivelayer.
 5. The high-sensitivity sensor of claim 3, further comprising:(d) a plurality of perforations through said locally resilient pressureconduction composite.
 6. The high-sensitivity sensor of claim 1, furthercomprising: (c) a plurality of perforations through said locallyresilient pressure conduction composite.
 7. A sensor array comprising aplurality of high-sensitivity sensors of claim
 1. 8. The sensor array ofclaim 7, further comprising a rigid element contacting one said locallyresilient conductive layer of each said high-sensitivity sensor.
 9. Asensor array comprising a plurality of high-sensitivity sensors of claim3.
 10. The sensor array of claim 9, further comprising a rigid elementcontacting one said locally resilient non-conductive layer of each saidhigh-sensitivity sensor.
 11. A high-sensitivity sensor comprising: (a)at least three locally resilient conductive layers; and (b) at least twolocally resilient pressure conduction composites each having a criticalpercolation threshold, each said locally resilient pressure conductioncomposite comprising a non-conductive matrix and a plurality ofconductive particles near said critical percolation threshold, each saidlocally resilient pressure conduction composite disposed between andcontacting two said locally resilient conductive layers.
 12. Thehigh-sensitivity sensor of claim 11, further comprising: (c) a rigidelement contacting one outermost said locally resilient conductive layeropposite of one said locally resilient pressure conduction composite.13. The high-sensitivity sensor of claim 11, further comprising: (c) apair of locally resilient non-conductive layers, each said locallyresilient non-conductive layer contacting one outermost said locallyresilient conductive layer opposite of said locally resilient pressureconduction composite.
 14. The high-sensitivity sensor of claim 13,further comprising: (d) a rigid element contacting one said locallyresilient non-conductive layer opposite of one said locally resilientconductive layer.
 15. The high-sensitivity sensor of claim 13, furthercomprising: (d) a plurality of perforations through said locallyresilient pressure conduction composites.
 16. The high-sensitivitysensor of claim 11, further comprising: (c) a plurality of perforationsthrough said locally resilient pressure conduction composites.
 17. Asensor array comprising a plurality of high-sensitivity sensors of claim11.
 18. The sensor array of claim 17, further comprising a rigid elementcontacting one outermost said locally resilient conductive layer of eachsaid high-sensitivity sensor.
 19. A sensor array comprising a pluralityof high-sensitivity sensors of claim
 13. 20. The sensor array of claim19, further comprising a rigid element contacting one said locallyresilient non-conductive layer of each said high-sensitivity sensor. 21.A high-sensitivity sensor comprising: (a) a locally resilient pressureconduction composite having a critical percolation threshold, saidlocally resilient pressure conduction composite comprising anon-conductive matrix and a plurality of conductive particles near saidcritical percolation threshold; (b) a flexible substrate completelysurrounding said locally resilient pressure conduction composite; and(c) a pair of electrical leads contacting said locally resilientpressure conduction composite within said flexible substrate andterminating outside of said flexible substrate.
 22. The high-sensitivitysensor of claim 21, further comprising: (d) a rigid element contactingsaid flexible substrate opposite of said locally resilient pressureconduction composite.
 23. The high-sensitivity sensor of claim 21,further comprising: (d) a plurality of perforations through said locallyresilient pressure conduction composite.
 24. A sensor array comprising aplurality of high-sensitivity sensors of claim
 21. 25. The sensor arrayof claim 24, further comprising a rigid element contacting said flexiblesubstrate of each said high-sensitivity sensor opposite said locallyresilient pressure conduction composite.
 26. A sensor array comprising aplurality of high-sensitivity sensors of claim
 23. 27. The sensor arrayof claim 26, further comprising a rigid element contacting said flexiblesubstrate of each said high-sensitivity sensor opposite said locallyresilient pressure conduction composite.